JPS63271722A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE:To decrease extra pulse errors by impressing an AC magnetic field to a magnetic coating compd. to disperse magnetic powder before the magnetic coating compd. solidifies. CONSTITUTION:The AC magnetic field is impressed to the magnetic coating compd. prepd. by dispersing the magnetic powder and binder together with other necessary additives into a volatile solvent and dispersing the mixture before the magnetic coating compd. solidifies on evaporation of the solvent or before said compd. is coated. Such magnetic coating compd. is continuously coated on a nonmagnetic base. For example, the magnetic coating compd. 1 is passed through an AC solenoid 4 to which AC is supplied by an AC power supply 5 and a filter 6 by a liquid feed pump 3 and thereafter, said compd. is coated on the nonmagnetic base. The extra pulse errors are thereby decreased and, therefore, the frequency of exchanging the filter is decreased and workability is improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing a magnetic recording medium using magnetic powder with excellent dispersibility. The present invention relates to improvements in methods for treating magnetic paints or magnetic recording media in the state of the art.

[Prior Art and its Problems] Generally, magnetic recording media such as magnetic tapes and flexible magnetic disks are made by recording magnetic powder in a volatile solvent on a non-magnetic support such as a polyester film.

It is manufactured by coating and drying a magnetic paint made by mixing and dispersing a binder and other necessary additives, but if there are foreign substances such as dispersions or reagglomerates of magnetic powder in the magnetic paint, Since this causes the generation of noise such as extra pulse error, which is a noise pulse after DC cancellation, a filter is used in the magnetic coating liquid delivery system immediately before coating to remove foreign substances from the magnetic coating.

However, the method using the filter has the following problems.

The smaller the pore diameter of the filter immediately before application, the more effective it is in removing foreign matter from the magnetic paint, but if the pore diameter is too small, the magnetic powder itself or additives intended to strengthen the durability of the magnetic layer, etc. In some cases, the performance of the magnetic recording medium cannot be maintained.

In addition, magnetic powder etc. tend to clog the filter, making it necessary to replace the filter frequently and stopping the applicator each time. Deteriorate.

However, in order to prevent noise increases such as extra pulse errors, in practice, filters have to be replaced frequently even if productivity is ignored. Therefore, there is an urgent need to develop a technology that can reduce the frequency of filter replacement during the coating process without impairing performance.

[Object of the Invention] The present invention has been made in view of the current situation, and it is an object of the present invention to provide a magnetic recording medium coated with a magnetic coating material in a stable dispersed state and with few extra pulse errors.

Another object of the present invention is to extend the service life of the filter in the coating liquid delivery system and to improve the operating rate and workability, such as reducing the frequency of filter replacement.

[Structure and operation of the invention] In order to achieve the above object, the present invention provides a method for manufacturing a magnetic recording medium in which a magnetic paint is applied on a non-magnetic support. The liquid is coated by applying an alternating magnetic field, dried completely, and subjected to calendering if necessary.

That is, the present invention uses magnetic powder in a volatile solvent.

The magnetic coating material dispersed together with the binder and other required additives is coated continuously on the non-magnetic support by applying an alternating magnetic field, before the solvent volatilizes and solidifies, preferably before coating. This is a method for manufacturing a magnetic recording medium, which is characterized in that the magnetic recording medium dries.

Hereinafter, the present invention will be explained with reference to the drawings.

FIG. 1 shows an example of an actual IM aspect of the present invention.

Magnetic powder, V3, in the volatile solvent sent from the previous process
The magnetic paint 1 uniformly dispersed together with the mixture and other necessary additives is led to a storage tank 2 and stored. Precipitates during storage,
Stir with a stirrer to prevent agglomeration.

The magnetic layer F11 is connected to the inside of the AC solenoid 4 and the filter 6 to which AC is supplied by the AC power source 5 by the liquid feeding pump 3.
After passing through it, it is coated on a non-magnetic support. AC 1
When the viscosity of the magnetic paint is adjusted to about 5 to 100 voids when applying the M lift, the magnetic powder can be well dispersed by the magnetic field.

By the way, the magnetic field strength of the alternating current magnetic field used in the present invention is
Viscosity of magnetic paint, flow opening,! iMagnetic particle size, shape, coercive force, etc., AC power frequency, passage length of AC magnetic field,! It varies depending on the field application time, etc., and should be determined through on-site tests, etc., but in practice it should be 35 Gauss to 700 Gauss, especially 1
0 Gauss to 350 Gauss is preferably used.

The AC power frequency is similarly related to the above factors, but 20Hz
A range of 50 KHz or more is preferably selected.

As the alternating current magnetic field generator, known means other than the above-mentioned alternating current solenoid can be used.

Examples of the magnetic powder used in this invention include 7-
Fe2O3 powder* Fe3O4 powder, C.

Various conventionally known magnetic powders such as Fe powder, Go powder, Fe--Ni powder, and other metal powders are widely included, as well as Fe3O4 powder containing 7 FezO3 powder and CoO-containing Fe3O4 powder.

In addition, examples of binders include vinyl chloride-vinyl acetate copolymers, cellulose resins, and butyral resins.

Any conventional binder resin such as polyurethane resin, polyester resin, epoxy resin, polyether resin, or isocyanate compound can be used.

Examples of volatile solvents include ketone solvents such as cyclohexanone, methyl ethyl ketone, and methyl isobutyl ketone;
Solvents suitable for dissolving the binder resin to be used, such as aromatic hydrocarbon solvents such as benzene, toluene, and xylene, sulfoxide solvents such as dimethyl sulfoxide, and ether solvents such as tetrahydrofuran and dioxane, are particularly limited. They can be used alone or in combination of two or more.

Further, various commonly used additives such as 111 lubricant, abrasive, antistatic agent, rust preventive, etc. may be appropriately added to the magnetic paint.

[Example 1] A magnetic paint having the following composition was prepared by a conventional method.

Co-adhered - FezOa (coercive force 60008° particle size 0
．． 4 μm.

Acicular ratio 7/1) 100 parts by weight Alumina 4 parts by weight Carbon black 10 parts by weight Dispersant
5 parts by weight urethane resin
32 parts Coronate Nippon Polyurethane Industrial Products) 10 parts Stearic acid ester 5 parts Cyclohexanone, methyl ethyl ketone.

Toluene mixed solvent 350@a part The magnetic coating liquid obtained in this way was stored in a storage tank 2 as shown in Fig. 1, and the internal dimensions were 250 mm in width, 40 mm in height, and 60 mm in depth, and the number of turns was 100. Using AC solenoid 4,
After applying the magnetic paint at a frequency of 601-1z and a field strength of 205 Gauss, the magnetic paint is continuously fed from a liquid pump, and is introduced into a coating machine through a filter 6 and coated on a polyethylene terephthalate film with a thickness of 75 μm after drying to a thickness of 1.
．． It was coated to a thickness of 5 μm.

After the magnetic particles in the magnetic layer coated on the base film were randomized in their orientation within the coated surface, they were led to a drying chamber, dried, and calendered.

A disk with a diameter of 13 Oam was beaten and polished, and then placed in a floppy disk jacket to prepare a sample.

[Example 21] An AC solenoid was installed in the circulation line as shown in Fig. 2 to the same magnetic coating liquid as in Example 1, and while the magnetic coating liquid was being circulated, the same AC magnetic field as in Example 1 was applied. Then, a part of the magnetic coating liquid from the circulatory system was extracted, and a sample was prepared after continuous application in the same manner.

[Example 3] An AC solenoid was installed in the same magnetic coating liquid as in Example 1, as shown in Figure 3, at a position before entering the drying room where the volatile paid solvent would not volatilize and the magnetic paint would not solidify. After applying the same alternating current magnetic field as @1 and performing the same coating, a sample was prepared.

[Comparative Example] A sample was prepared by applying the same magnetic coating liquid as in Example 1 without applying an alternating magnetic field.

Regarding the magnetic recording media of Example 1.2.3 and Comparative Example obtained as follows, the measurement results of extra pulse error and the discharge pressure of the filter in the above operation were 5 K'
The elapsed time to reach J/cti is shown in Table 1.

Table 1 Note that the extra pulse records a magnetic flux reversal frequency of 250,000 magnetic flux reversals/second, then performs DC erasure, so that the peak area of the reproduced signal is 1/2 of the average signal double width.
It was assumed that the signal exceeded 0%, and the extra pulse error was determined by measuring the extra pulses of all tracks, and taking the ratio of samples in which one or more signals occurred as extra pulses.

In addition, the reason why we evaluated the elapsed time when the discharge pressure of the filter reached 5 kg/- was that the clogging of the filter during the filtration process in this experiment gradually increased, and the discharge pressure decreased to 5 kg/-.
If the discharge pressure approaches 5 kg/cd, the filter must be replaced, as there is a risk of pipe rupture exceeding Kg/cd or foreign objects larger than the pore diameter of the filter being forced through, and the frequency of filter replacement may be reduced. This is because it serves as a guideline.

As is clear from Table 1, Example 1. The method of Example 2゜Example 3 has less extra pulse error than the method of Comparative Example, and the method of Example 1゜2 has a longer time to reach the filter 5 kg/d, which reduces the frequency of filter replacement. , workability has been greatly improved. This shows that the method of this example is superior to the comparative example.

[Brief explanation of drawings]

1 to 3 are process schematic diagrams showing embodiments of the present invention. In the drawing, 1 is a magnetic paint and 2 is a storage tank. 3 is a transport pump, 4 is an alternating current magnetic field, 5 is a magnetic field generating power source (alternating current), and 6 is a filtering means.

Claims (13)

[Claims] (1) Magnetic paint obtained by dispersing and dissolving magnetic powder, binder, and additives in a volatile solvent is applied to a non-magnetic material, and the solvent is evaporated to solidify the magnetic paint to form a magnetic recording medium. A method for manufacturing a magnetic recording medium, which comprises applying an alternating magnetic field to the magnetic paint to disperse the magnetic powder before the magnetic paint solidifies. (2) The method for manufacturing a magnetic recording medium according to claim 1, wherein an alternating current magnetic field is applied to the magnetic paint before it is applied to the non-magnetic material. (3) A method for manufacturing a magnetic recording medium according to claim 1, wherein an alternating magnetic field is applied to a magnetic paint coated on a non-magnetic material. (4) The method for manufacturing a magnetic recording medium according to claim 1, wherein the alternating current magnetic field applied to the magnetic paint is in the range of 35 to 700 Gauss. (5) The AC magnetic field applied to the magnetic paint is 20Hz to 50K.
Hz. The method for manufacturing a magnetic recording medium according to claim 1 or 4. (6) The method for manufacturing a magnetic recording medium according to claim 1, 4, or 5, wherein the alternating current magnetic field uses an alternating current solenoid as a magnetic field generating device. (7) Magnetic powder is γ-Fe_2O_3 powder, Fe_3O
_4 powder, Co-containing γ-Fe_2O_3 powder, Co-containing Fe_3O_4 powder, Fe powder, Co powder, Fe-Ni
The magnetic recording according to claim 1, wherein the magnetic recording material is at least one selected from powder and Fe containing Al, Cr, Mn, Si, Zn, etc., and is dispersed in a magnetic paint. Method of manufacturing media. (8) The binder is selected from the group of vinyl chloride-vinyl acetate copolymer, cellulose resin, butyral resin, polyurethane resin, polyester resin, epoxy resin, polyether resin, and isocyanate resin. 2. The method for manufacturing a magnetic recording medium according to claim 1, wherein at least one type of resin is used. (9) The solvent is cyclohexanone, methyl ethyl ketone,
Ketone solvents such as methyl isobutyl ketone, benzene,
The method for producing a magnetic recording medium according to claim 1, which contains any one of an aromatic hydrocarbon solvent such as toluene and xylene, a sulfoxide solvent such as dimethyl sulfoxide, and an ether solvent such as tetrahydrofuran and dioxane. (10) The method for producing a magnetic recording medium according to claim 1, wherein the additive is at least one member of the group consisting of a lubricant, a thickener, an abrasive, an antistatic agent, and a rust preventive. (11) The method for manufacturing a magnetic recording medium according to claim 2, wherein the magnetic coating material when applying an alternating magnetic field has a magnetic strength in the range of 5 to 100 poise at a temperature of 25°C. (12) A method for manufacturing a magnetic recording medium according to claim 1, wherein the magnetic coating liquid before being applied to the non-magnetic material is filtered by a filtration means. (13) A method for manufacturing a magnetic recording medium with less noise including extra pulse errors obtained by the means described in any one of claims 1 to 12.